Refactor version resolution logic into helper functions (#2)

## Summary

Refactor the action script by moving the version resolution workflow out
of `scripts/main.ps1` and into a dedicated `scripts/Helpers.psm1`
module.

This keeps `main.ps1` as a thin orchestrator and makes the individual
steps easier to read, compare, and validate.

## Changes

- extract action input parsing into `Read-ActionInput`
- extract publish settings parsing into `Get-PublishConfiguration`
- extract pull request event loading into `Get-GitHubPullRequest`
- extract release decision logic into `Resolve-ReleaseDecision`
- extract GitHub and PowerShell Gallery version lookups into dedicated
helpers
- extract next-version calculation and action output writing into
dedicated helpers
- update `scripts/main.ps1` to orchestrate the helper calls

## Notes

- Intended behavior is unchanged for the normal release/version
resolution path.
- Error handling now throws from helper functions instead of using
inline `Write-Error`/`exit` in `main.ps1`.

## Validation

- verified the refactor against `main` with `git diff
--function-context`
- verified both edited PowerShell files report no editor errors locally

Author: MariusStorhaug